The invention relates to techniques for controlling entry of terminals in wireless communication networks such as mobile communication networks.
Network Entry is the procedure by means of which a terminal (mobile or fixed) “enters” a wireless communication network including any number of base stations. Basic telecommunication standards such as 802.16-2004 and 802.16-2005 specify the steps necessary to complete this task, i.e., Network Entry. One of the key factors that come into play in the related procedure is the maximum transmission power allowed for a terminal entering the network.
During normal operation, that is, once the terminal has already entered the network, the power level of the terminal is adjusted as a function of measurements performed at the base station. Conversely, during the initial steps of the Network Entry procedure, e.g., Initial Ranging, the maximum allowed power is determined by the terminal itself. For instance, the terminal seeking entry to the network may calculate a value for its maximum allowed power PTX—IR—MAX on the basis of the following relationship:PTX—IR—MAX=EIRxPIR,max+BS—EIRP−RSS+(GRx—SS−GTx—SS)
where:                EIRxPIR,max is the maximum equivalent isotropic received power at the terminal, that is the effective power measured at the antenna receiver,        RSS is the received signal strength at the antenna output,        BS_EIRP is the equivalent isotropic radiated power of the base station, that is the effective power measured at the antenna transmitter, and        GRx—SS and GTx—SS are the receiver and terminal antenna gain at the terminal.        
The terminal will start the network entry procedure by using a given power level, e.g., the level PTX—IR—MAX calculated as indicated in the foregoing or, e.g., in case this value cannot be calculated, a minimum reference level (which may be lower than PTX—IR—MAX).
Typically, during the Network Entry procedure, the terminal attempts to establish communication with the base station expected to serve it until it receives a response from the base station. In so doing, the terminal starts from a given initial power level, and, in case no response is received from the base station, the terminal gradually increases its transmission power up to a maximum value, and possibly “wraps back” to the initial value, restarting the procedure from the beginning, if no response is received from the base station.
Typically, after a given number of repeated attempts without being able to establish communication (i.e., without network entry being achieved) a back-off procedure is initiated: since a limited number of entries is available, the terminal generates a random number in order to determine the entry to be used for network entry. In case of failure, a new number is tried up to a maximum number of retry attempts. Once this maximum number is reached, the channel is “marked” as unusable and the terminal looks for a new channel where the Network Entry procedure is re-started from the beginning.